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The Anatomy of the Gum*

Marcos Gridi-Papp

This work is produced by OpenStax-CNX and licensed under the Creative Commons Attribution License 4.0„

Abstract The gingiva is the part of the masticatory mucosa that surrounds the teeth and extends to the alveolar mucosa. It is rmly attached to the jaw bone and it has keratinized stratied squamous epithelium. The free gingiva is separated from the tooth by the gingival groove and it it very narrow. Most of the gum is the attached gingiva. The interdental gingiva occupies the cervical embrasures in healthy but may cause it to receede. Gingival bers attach the gums to the neck of the tooth. They also provide structure to the gingiva and connect the free to the attached gingivae.

Figure 1: Maxillary gingiva of a dog. More details1.

This chapter is about the gums, which are also called gingivae (singular gingiva). The text will describe the structure of the gingiva and explain its role in periodontal diseases, from to abscesses in humans and other mammals. *Version 1.1: Mar 3, 2018 8:43 pm -0600 „http://creativecommons.org/licenses/by/4.0/ 1https://upload.wikimedia.org/wikipedia/commons/3/3b/Bull_Terrier_Chico_05.jpg

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1 Structure The gingiva is part of the masticatory mucosa2 of the mouth. This mucosa is formed by keratinized stratied squamous epithelium and it covers the dorsum of the and hard in addition to forming the gingivae.

Figure 2: The gingiva surrounds the teeth and contacts the alveolar mucosa. More details3.

The gingivae surround the teeth and provide a seal around each of them. They are tightly bound to the underlying bone. This helps them resist friction against food during mastication. A healthy gingiva is an eective barrier against external threats to deeper tissue. The gingiva interfaces with the alveolar mucosa which is non-keratinized, darker and much looser as a lining of the oral cavity than the masticatory mucosa (Fig. 2). The line of contact between the gingiva and the alveolar mucosa is called . Healthy gums range from light pink to tan depending on the person's skin color. Accumulation of bacterial plaque4 , however, can cause inammation with increased redness together with swelling and a tendency to bleed. A chronic inammation of the gingiva can aect the deeper tissue of the periodontium5 and potentially compromise the tooth. The gingiva is divided anatomically into three areas called free (marginal), attached and interdental gingivae (Fig. 3).

2https://en.wikipedia.org/wiki/Oral_mucosa 3https://upload.wikimedia.org/wikipedia/commons/4/43/NIH_DOC_7_gingiva.jpg 4https://en.wikipedia.org/wiki/Dental_plaque 5https://en.wikipedia.org/wiki/Periodontium

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1.1 Free gingiva The free (also called marginal) gingiva is the edge of the gingiva, the portion where it is not attached to the tooth (free in this case refers to not attached). It is delimited by the free gingival groove, a shallow depression on the surface of the gum that is visible in about half of the population. This groove is most prominent in mandibular incisors, canines and premolars.

Figure 3: The anatomical structure of the gingiva. More details6.

The free gingiva varies in width from 0.5 to 2 mm from the free gingival crest to the attached gingiva. The marginal gingiva has a similar appearance to that of the attached gingiva being slightly more translucent. The free gingiva lacks (textured surface), however, and it is more movable for not being attached the underlying tooth. The free gingiva is stabilized by gingival bers7 that have no bony support. The , or free gingival crest is the most coronal part of the free gingiva. The is the space between the free gingiva and the tooth.

1.2 Attached gingiva The attached gingiva is continuous with the free gingiva. It is rm, resilient, and tightly bound to the underlying periosteum of alveolar bone. The facial aspect of the attached gum extends to the relatively loose and movable alveolar mucosa8 with the limit marked by the mucogingival junction9 . The attached gingiva frequently presents surface stippling10 , a roughened texture that derives from the organization of epithelial ridges and dermal papillae. The degree of stippling is highly variable among individuals. The attached gingiva is widest in the incisor region (3.5 to 4.5 mm in the maxilla and 3.3 to 3.9 mm in the mandible) and narrowest in the rst premolar region (1.9 mm in the maxilla and 1.8 mm in the mandible).

6https://upload.wikimedia.org/wikipedia/commons/c/ca/Healthy_gingiva.jpg 7https://en.wikipedia.org/wiki/Gingival_bers 8https://en.wikipedia.org/wiki/Alveolar_mucosa 9https://en.wikipedia.org/wiki/Mucogingival_junction 10https://en.wikipedia.org/wiki/Stippling_(dentistry)

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Figure 4: Stippling may be visible as a texture on the surface of the attached gingiva but not of the free gingiva, which is always smooth. More details11.

1.3 Interdental gingiva The interdental gingiva12 (also called ) lies between the teeth occupying the gingival embrasure13 , which is the close proximity space apical to the area of tooth contact. This gingiva tends to have a pyramidal shape in the vestibular and in the lingual aspects with a less extended ridge between them, forming a concave structure.

1.4 Gingival bers The gingiva14 is held rmly against the tooth by gingival bers15 composed of connective tissue16 . These bers dier from those of the periodontal ligament17 in attaching the tooth to the gingival tissue rather than to the alveolar bone18 . Gingival bers have several roles:

• They connect the base of the free gingiva19 to the tooth. 11https://upload.wikimedia.org/wikipedia/commons/c/cf/Stippled_gingiva.JPG 12https://en.wikipedia.org/wiki/Interdental_papilla 13https://en.wikipedia.org/wiki/Embrasure_(dental) 14https://en.wikipedia.org/wiki/Gingiva 15https://en.wikipedia.org/wiki/Gingival_bers 16https://en.wikipedia.org/wiki/Connective_tissue 17https://en.wikipedia.org/wiki/Periodontal_ligament 18https://en.wikipedia.org/wiki/Alveolar_bone 19https://en.wikipedia.org/wiki/Free_gingival_margin

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• They provide internal structure to the free gingiva to help it withstand the forces of mastication20 . • They reinforce the connection between the free and the attached gingivae.

Damage to the gingival bers promotes periodontitis21 . With reduced ber anchorage, the gingival sulcus22 (labeled G in the Fig. 5) broadens and increases in depth apically. This facilitates the entrance of debris and bacteria23 between the root of the tooth and the alveolar bone.

20https://en.wikipedia.org/wiki/Mastication 21https://en.wikipedia.org/wiki/Periodontitis 22https://en.wikipedia.org/wiki/Gingival_sulcus 23https://en.wikipedia.org/wiki/Bacteria

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1.4.1 Types of gingival bers

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Figure 5: The bers of the attach the tooth to the alveolar bone (periodontal ligament) and to the gingiva (gingival bers). A. Enamel. B. Dentin. C. Alveolar bone. D, Subepithelial connective tissue. E, Oral epithelium. F. Free gingival margin. G. Gingival sulcus. H. Principal gingival bers. I. Alveolar crest bers of the periodontal ligament (PDL). J. Horizontal bers of the PDL. K. Oblique bers of the PDL. More details24. OpenStax-CNX module: m66361 7

Gingival bers are arranged in three groups:

• Dentogingival group - there are three types of bers within this group: · Fibers that extend towards the free margin of the gingiva; · Fibers that extend laterally to the outer surface of the gingiva; and · Fibers that extend laterally past the alveolar crest, and then apically along the cortex of the alveolar bone25 . • Circular group - bers found entirely within the gingiva with no connection to the tooth. • Transseptal group - bers that make mesiodistal connections between teeth. They are mostly found in the gingiva between teeth but also extend through the gingiva around teeth.

1.4.2 Figure credits Figure 1 by Ivob - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4675607 Figure 2 Modied from original by BodyParts3D/Anatomography  http://www.nidcr.nih.gov/oralhealth/topics/oralcancer/detectingoralcancer.htm, Public Domain, https://commons.wikimedia.org/w/index.php?curid=34010997 Figure 3 Modied from original by Mohamed Hamze - taken in my private clinical practice, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3304239 Figure 4 by DRosenbach (talk). - DRosenbach (talk), Public Domain, https://commons.wikimedia.org/w/index.php?curid=8985701 Figure 5 by Goran tek-en - Own work. This vector image includes elements that have been taken or adapted from The Periodontium.jpg. This vector image includes elements that have been taken or adapted from Cross sections of teeth.svg., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=30709759

24https://upload.wikimedia.org/wikipedia/commons/9/92/Periodontium.svg 25https://en.wikipedia.org/wiki/Alveolar_bone

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